In this image taken from video obtained from Syrian opposition news outlet Ugarit News, which has been authenticated based on its contents and other AP reporting, smoke and fire fill the skyline over Damascus on May 5, 2013, after an Israeli air strike

After two air strikes inside Syria in the space of three days, Israel remains intent on targeting advanced weapons there before they can be transferred to Hizballah in Lebanon, Israeli military officials tell TIME. “It’s not over,” says one senior officer, who spoke on condition of anonymity because Israel has not officially acknowledged either of the strikes. “This is not the last incident.”

The savage civil war inside Syria has both emboldened Israel to act against existing threats and created new ones. Officials are concerned that as the Syrian state devolves into chaos, sophisticated weapons not previously available to Hizballah will make their way across the border to Lebanon, altering the military equation between Israel and the well-armed Shi‘ite militia sponsored by Iran and aided by the Syrian government.

One such weapon is the Fateh-110 missile, which Israel targeted in warehouses at Damascus International Airport on Thursday night and at the sprawling military compound in the Jamraya district outside the capital on Sunday night. Made by Iran, the Fateh, which means conqueror in Persian, has a range of 300 km (190 miles), easily enough to reach Israel’s major population centers from Lebanon. More worrisome, according to Israeli officials, is that the Fateh is highly accurate — able to deliver 600 kg (1,300 lb.) of high explosives within accuracy of 200 m (650 ft.), close enough to endanger strategic targets such as power plants, or the Defense Ministry headquarters in central Tel Aviv. (By contrast almost all of the other estimated 40,000 missiles already in Hizballah’s control are unguided.) Secondary explosions visible in videos posted online from Syria indicated the weekend air strikes struck munitions stockpiles.

Israeli pilots also targeted warehouses suspected of containing Yakhont shore-to-sea cruise missiles. Made by Russia, the supersonic missiles also known as P-800 Oniks travel at Mach 2, twice the speed of sound, and would endanger Israeli warships, as well the country’s offshore natural-gas platforms located near Lebanon. Israeli officials worry about the consequences of either weapon reaching Hizballah or falling into the hands of extremist Islamists fighting to depose Syrian President Bashar Assad, which include militant groups formally aligned with al-Qaeda.

“We prefer they burn,” the Israeli military official tells TIME. “That way nobody will be able to use them.”

In the past, Israel felt constrained from launching overt military strikes on Syria for fear of provoking retaliation. When Israel sent F-16s to destroy a nuclear reactor in the Syrian desert in 2007, it took pains to keep the operation secret — it took a week for the first reports to filter out — for fear of forcing Assad to respond in order to save face, according to reporting by David Makovsky in the New Yorker.

But a civil war that has gone on for more than two years has changed Israel’s calculus. Israeli officials are betting that Assad will not retaliate, both because his forces have their hands full already and because any strike against Israel would risk Israeli counterstrikes that might seriously degrade his advantages in the civil war, like airpower. “They don’t want to open a new front that might be the last one they open,” says one Israeli military official. “They would suffer a knockout punch.” One measure of Israel’s confidence was the whereabouts of its Prime Minister: Benjamin Netanyahu left on Sunday for a long-scheduled state visit to Beijing.

Still, in the wake of the strikes, Israeli forces went on heightened alert. A TIME correspondent hiking on Mount Meron in the Golan Heights heard the wail of sirens sounding several times Saturday morning on a forward Israel Defense Forces air base. Military sources said the sirens summoned all personnel to action stations, apparently in readiness for any military reprisal from the Syrian side.

“The question everybody is asking today is, ‘Is there going to be a war?’’’ says Benedetta Berti, a researcher at the Institute for National Security Studies, a think tank associated with Tel Aviv University and heavily staffed with former Israeli security officials. Berti said she heard the same question after Israeli jets struck inside Syria in late January, destroying a convoy carrying advanced SA-17 antiaircraft missiles toward Lebanon, damaging a chemical-and-biological-weapons research center and killing a senior Hizballah commander, intelligence sources tell TIME.

“At the end of January my answer was no, and that’s my answer this time, but it’s a lot less confident,” says Berti. “The Israelis are very clear that they don’t want to get involved [in the civil war] and this is very low cost. Assad is busy. But if you push it too much, eventually some sort of reaction will have to come.”

Israeli military officials say they will likely keep launching attacks, partly because Iran has stepped up the pace at which it’s arming Syria and Hizballah. “They’ve increased the number of shipments lately,” one says. But the strikes are also driven by Israel’s determination to act when it has actionable intelligence. “The problem is intelligence doesn’t always arrive smoothly and on time,” says one military official. The official says “some” earlier-generation Fateh-110s reached Hizballah in the past, before Israel could act.

“It’s always a balance: What’s the cost?” says Berti. “Assad was always risk-averse.” But when there were credible reports that Scud missiles had traveled from Syria to Hizballah — and even rumors of chemical weapons, Berti says — Israel took no overt action.

“I think what’s changed today is there’s really this perception that central control is breaking down [inside Syria],” says Berti. In other words, concerned parties still know where to look for the weapons that worry them most. That could change if Assad’s forces are overrun, or simply give up their positions. “Then we’ll have to worry that there is no address,” says Berti.

Karl Vick has been TIME's Jerusalem bureau chief since 2010, covering Israel,the Palestine territories and nearby sovereignties. He worked 16 years at the Washington Post in Nairobi, Istanbul, Baghdad, Los Angeles and Rockville, MD.